A package is known in the art as being a container in the form of a flexible bag or rigid walled housing provided with an opening that serves to provide access to the interior of the container. A lid or cover sheet is positioned over the opening and bonded to the container, typically by heat sealing, to enclose and seal the container interior and its contents from the external environment.
Blister packages suitable for the packaging and storing of food and drink, medicaments and other products have to comply with specific requirements in terms of barrier properties against moisture and gases, in particular oxygen, to firstly prevent ingress of moisture and gases through the packaging walls into the packaged products and secondly from the inside of the packaging into the surroundings.
By way of example, a wide variety of medicaments require to be stored into packages typically exhibiting water vapour permeability values below 0.06 g/(m2×24 h), preferably below 0.04 g/(m2×24 h).
Blister packages usually comprise two sheets which are firmly bonded to each other: a first base sheet containing cavities matched to the products to be packed, which is obtained typically by thermoforming a flat, preferably optically transparent, thermoplastic polymer film, and a second lid sheet, which, after the products have been properly fed to the preformed base sheet, is sealed onto the base sheet typically by heat sealing.
The base sheet commonly accounts for 80-85% by weight of the total weight of the blister package and the lid sheet commonly makes up the remaining 15-20% by weight of the total weight of said blister package.
Blister packages are commonly referred to as push-through packages if the packaged products can be pushed through the lid sheet by pressure on the base sheet and removed individually from the blister package.
Otherwise, blister packages are commonly referred to as peel-push packages if the lid sheet can be at least partially peeled off before removal of the packaged products by pushing against the base sheet.
The base sheet is usually optically transparent but it can be obscured for use in child-resistant packages or to protect light-sensitive drugs.
Several thermoplastic polymer films are commonly used for this purpose. Polyvinylidene chloride (PVDC) and polychlorotrifluoroethylene (PCTFE) polymers are particularly suitable for use in the manufacture of optically transparent base sheets for blister packages due to their low permeability to moisture and/or gases, in particular oxygen.
For instance, U.S. Pat. No. 4,424,256 (AMERICAN CAN COMPANY) Jan. 3, 1984 discloses a heat sealable flexible packaging film comprising a heat sealable layer (12) made from a linear low density polyethylene, an adhesive layer (14) made from a blend of 20% to 80% of a linear low density polyethylene and 80% to 20% of a propylene ethylene copolymer, a layer (16) made from an anhydride-modified propylene-based primer and a layer (18) made from an aluminium foil. An additional layer (20) of a protective polymeric material may be present on the surface of the layer (18) opposite to the layer (12). The sheet may be readily made into a pouch, said pouch being suitable for packaging products which will be subjected to a sterilizing process after the product is put into the package and the package is sealed.
Also, U.S. Pat. No. 6,270,869 (ALUSUISSE TECHNOLOGY MANAGEMENT LTD.) Aug. 7, 2001 discloses a laminate film for a push-through or a blister pack, said laminate film comprising, in succession, a plastic layer made from any of a polyvinylchloride, a polyester, a polypropylene, a polyamide or a cyclo-olefin copolymer, a metal foil and an oriented polyamide film having a thickness of from 25 μm to 32 μm. The metal foil may be pre-treated with a primer on one or both its sides.
Further, U.S. Pat. No. 5,250,349 (MITSUI PETROCHEMICAL INDUSTRIES, LTD.) Oct. 5, 1993 discloses a laminate for a package, said laminate comprising a thermoplastic resin layer which is adhered to a metal layer through an adhesive resin composition comprising, inter alia, 1 to 15 parts by weight of a polyethylene graft-modified with an unsaturated carboxylic acid or a derivative thereof.
However, optically transparent base sheets having water vapour permeability values below 0.06 g/(m2×24 h) are commonly achievable by using PCTFE films having a thickness greater than 100 μm.
On the other side, aluminium films are typically used as lid sheets which advantageously have water vapour permeability values below 0.04 g/(m2×24 h).
However, aluminium films are not optically transparent and have low deformability, and cannot therefore be used to produce relatively small blister packages.
It is also desirable that the lid sheet of a peel-push blister package maintains its integrity during the opening of the package and during the full lifetime of use of the blister package such as during any coiling or winding up of the lid sheet once separated from the base sheet.
To override the drawbacks of the blister packages of the prior art, lid sheets have been developed in the form of laminates with plastic films comprising, inter alia, aluminium layers. See, for instance, US 2011/0210037 (J. MUENSTER ET AL.) Sep. 1, 2011 and US 2008/0251411 (GLAXOSMITHKLINE CORPORATE) Oct. 16, 2008.
There is nevertheless still the need in the art for thermoplastic polymer material-based film assemblies providing for packages having high barrier properties from the external environment, low thickness, good optical transparency and good sealability, while maintaining good interlayer adhesion properties, and for a cost-effective and environmentally friendly process for the manufacture of said packages allowing the lowest possible consumption of raw materials.